The present invention relates generally to low power equipment such as telecommunications systems, displays, and the like, ranging from cell phones to simply battery powered devices, in which amplification is necessary and in which either power consumption or stable operation in an integrated circuit in its quiescent state is an important consideration. The present invention involves a variety of designs which provide alternative techniques to achieve bias control in a variety of amplifier arrangements.
Supply voltages in electronic equipment are continually decreasing. Logic circuits are continually using faster but lower breakdown devices, forcing supply voltages lower. Battery powered circuits such as wireless telephones use the lowest practical voltage to minimize power consumption. This makes it imperative for analog circuitry to make use of every bit of the supply voltage range, and has caused the creation of rail-to-rail gain stages, which can swing almost from one supply voltage rail to the other. This is especially important in low power devices, that is, devices in which power consumption is an important consumer or user consideration and/or desire.
A problem with building amplifiers with rail-to-rail gain stages, however, is that they tend to be much more complex than traditional amplifiers. Large signal swings in an output stage can be accommodated most easily by making the output stage a common emitter gain stage. When implemented in a complementary form (with both pnp and npn devices), some form of bias control circuitry is needed, which adds complexity to the circuit. The bias control circuit also adds another feedback loop requiring stabilization and isolation from the input signal feedback loop.
While there have been a variety of solutions proposed for such designsxe2x80x94and while those solutions achieve their various goals to a large degree, to date no single design achieves its goals in a design which provides the simplicity and the alternative designs of the present invention. As but one example, one design is set forth in U.S. Pat. No. 5,521,553, hereby incorporated by reference. As that example explains, there have been a variety of efforts, yet there still remains room for improvement from a practical perspective whether it be in minimizing complexity, reducing component count, to achieve even more stable operation, or the like. Similar efforts are detailed in U.S. Pat. Nos. 5,440,273, 5,786,731, 5,162,751, 4,335,358, and 5,734,296. All the foregoing references are hereby incorporated by reference. Thus, even though solutions to the problems mentioned in this disclosure have existed, to date none are believed to have provided the proper balance of competing concerns in most applications and certainly none have met the various criteria now metxe2x80x94especially in the telecommunications device area or the like.
Further, the present invention shows that alternative designs can be accomplished with different attributes than those previously existing. For some particular applications, these designs could be critical to their specific goals. To some degree the designs disclosed show that in spite of a long felt but unsatisfied need for additional designs and attributes, there are in fact, other designs which were available. These even may be viewed as implementing arts and elements which had long been available, but were not realized in the past. Perhaps to some degree, those skilled in the art did not appreciate or even realize the existing problem. It may even be true that those involved in this field simply taught away from the technical direction in which the inventor went with this invention, that they did not expect the results now achieved, or that they did not believe such results could be achieved in this fashion.
The present invention discloses both methods and embodiments of apparatus for providing telecommunications equipment or the like and perhaps even for generally biasing an amplifier stage which may result in high signal gain, stable quiescent bias, and which controls the current in the quiescent state. The alternative apparatuses and methods for biasing the electronic gain stage can achieve not only a stable operation and provide useful alternatives, they can also meet several practical considerations. Specifically, in various embodiments, the invention focuses on circuit techniques useful in biasing a common emitter gain stage in an integrated circuit amplifier as may be used in battery powered devices, telecommunications equipment, or the like. In some of the embodiments disclosed, a key to effective bias control can lie in minimizing the number of transistors needed and in keeping the effects of input signal changes and bias control changes orthogonal. A basic method in these embodiments can consist of controlling the input of the gain stage 103 by balancing two signals against each other, a bias reference signal 101 and a feedback signal representing the bias in the gain stage 102 as shown in FIG. 1. The reference signal may be made up of a bias reference signal combined with an input signal in such a manner that the input signal has high gain to the output and the reference signal has low gain to the bias point. Naturally, the feedback signal representing the bias in the gain stage 102 may take several forms, depending on the desired result.
Accordingly, the present invention advantageously provides a simple method of controlling the bias in the gain stage without decreasing the high gain desired for signals. This may allow, for instance, the easy introduction of the desired temperature coefficient to the gain stage bias without degrading the signal gain.
Another advantage of the present invention is that several possible control methods can be used for the gain stage bias. These methods can include techniques such as Geometric Mean Biasing or Harmonic Mean Biasing, as well as other methods.
Naturally further objects of the invention are disclosed or should be understood throughout other areas of the specification and drawings.